Treatment of magnesium and magnesium alloys to inhibit corrosion



Patented July 17, 1928.

UNITED STATES PATENT (OFFICE.

Autumn; o. zI uMnnMAN, or DAYTON, oar 0.1

TREATMENT or No Drawing.

This invention relates to the treatment of magnesium and magnesium alloys, so as to inhibit or prevent corrosion, 1 to which metals of this type are quite susceptible.

I have discovered that if an article made of magnesium ormagnesium alloys in which magnesium is present as the major constituent, are subjected to the action of a dilute solution of phosphoric acid, boric acid, borax or other borates of the alkali metals, a coating or impregnation of phosphate, borate, or other compound of magnesium likely to form under the treatment, is produced. It isv also desirable to have present in the treating solution, an oxidizing salt such as manganese dioxide. As an example of a treatment which affords ample protection, the following is submitted: The material is immersed in a .75 per cent by volume solution ofphosphoric acid, containing about 1 ounce of manganese dioxide per gallon' of solution. At the time the metal is immersed the solution should'be heated to about 200 Fahrenheit, and this temperature maintained after the immersion of the metal, which remains immersed until a continuous coating or impregnation. ofthe dark gray colored compound of magnesium is formed,'or until practically all gas ceases to be evolved from'this solution. Usually about one and one-half hours are suflicient for the complete treatment of the metal in the solution.

The metal is' then removed from the solution and washed with water. After the washing with water, it is heat-treated by placing it in an oven. After bakingfor a short time, suficiently to thoroughly dry it is removed and and stabilize the coating,

Subsequently cooled to room temperature.

a coating or coatings of paint, enamel or lac-- quer, or combinations thereof are applied, depending upon'the results desired. It has been found that, for inhibiting corrosion when exposed to the atmosphere, salt water, benzol or gasoline, two coatings of bakelite lacquer serve the purpose excellently as a finishing coating metal.

' metal. Very good results merely subjecting the metal to the action of magnesium base alloys A lthough the protection afforded by sub-" sequent heat treating and painting is greatly improved thereby, these twosteps are not absolutely essential in the treatmentof the the phosphoric acid, borioacid or borax as are obtained by 3.

MAGNESIUM Ann MAGNESIUM ALLOYS 'ro mnmrr CORROSION.

Application filed October. 31, 1924. Serial No. 747,128.

the case may be, and merely 'washing or drying the treated metal.

It is essential that the solution of acid used be sufliciently Weak so asto prevent too rapid action on the metal. In case the acid is stronger than it should be, .the acid eats into the metal so rapldlythat the scales or protective coating is loosened and does not rigidly adhere to the product. It has been found that a to a 1 per cent solution of phosphoric acid is most desirable, but if the time is increased considerably, a weaker solution than to 1 per cent may be used. Similarly it is possible to use more than a 1 per cent solution of phosphoric acid; for a shorter period of time, although in suchcase the protective. coating is not quite as integral as the coating which would be produced more slowly.

When boric acid is used in place of phosphoric acid as the treating acid, the solution should beslightly stronger than 1 per cent, as the boric acid is not quite so active an agent in attacking magnesium. Less thana 5 per cent solution however should be used. In-the case of borax, it has been found that less than a 5 per cent solution should be used for the-best results, but'this salt also may be slightly stronger than the solution of phosphoric acid used.

The saltsformed on thesurface of the magnesium article treated are of an insoluble medium and are quite stable and serve to adequately protect the material beneath it. They also form asurface to which the paint or lacquer may be effectively applied.

I-claim:

1. The method of treating magnesium and magnesium base alloys to inhibit corrosion, comprising treating the metal with a solution of not more than five percent phosphoric acid containing from one-tenth to ten ounces manganese dioxide per gallon of solution for about one and one-half hours.

2. The method of treating magnesium and magnesium base alloys to inhibit corrosion,

compris ng treating the metal with .a solution of not more than five percent phosphoric acid, for about one and one-half hours at a temperature of about 200 Fahrenheit in the presence of from one-tenth to ten ounces manganese dioxide per gallonofsolution,

The method of treating magnesium and to inhibit corrosion against natural and prepared agencies, comtreated metal and coating with paint or lacquer; Y

4. The method of treating magnesium -ar- .ticles. comprising treatingthe article inawater solution of less than"5.per cent of phosphoric acid, for about one. and one-half hours at about 200 Fahrenheit in the presganese dioxide per gallon of solution' and subsequently drging the article. 4

5. The metho of treating magnesium and magnesium base 'alloys to inhibit corrosion ,ence; of from one-tenth to ten ounces manwhich consists of-treating the metal with a solution of phosphoric .acid until as protective coating of magnesium' phosphate is formed on the surface of the metal.

In testimony whereof I. afiix'my signa ture. A

' ARTHUR C. ZIMMERMAN. 

